1. Field of the Invention
The present disclosure relates to an image forming apparatus and a process cartridge. Herein, the image forming apparatus forms an image on a recording medium using an electrophotographic image forming process. Examples of the image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (an LED printer and a laser beam printer and the like), and a facsimile machine.
2. Description of the Related Art
In an image forming apparatus using a conventional electrophotographic image forming process, a photosensitive drum and a process unit (for example, a developing unit, a charging unit, a cleaning unit) acting on the photosensitive drum are integrated as a cartridge. A cartridge method is employed, which detachably attaches the cartridge to the main body of the image forming apparatus.
Because the maintenance of this kind of process cartridge in the apparatus can performed by a user himself without depending on a service staff, the operability thereof can be improved. Then, the cartridge method is widely used in an electrophotographic image forming apparatus.
Hereinafter, the conventional image forming apparatus will be described. A cartridge obtained integrally combining a photoreceptor unit with a developing device unit is known as the conventional process cartridge. The photoreceptor unit is obtained by integrally unitizing a photosensitive drum and a cleaning unit and the like. The developing device unit is obtained by unitizing a developing roller and a toner containing container and the like. In this process cartridge, the photoreceptor unit is configured by attaching the photosensitive drum, the charging unit, and the cleaning unit to a drum frame body. The developing device unit is configured by incorporating a developing blade and a toner conveyance stirring unit in addition to the developing roller and the toner containing container. The process cartridge is formed by integrally joining both the side surfaces of the photoreceptor unit and the developing device unit, using a side cover including a ventilation hole, and the like.
In the conventional image forming apparatus, an electrostatic latent image is formed on the photosensitive drum by a charging device and an exposure device and the like. A developer is applied by a developing device, to allow the electrostatic latent image to be a visible image (developer image). The developer image (toner image) is transferred to a transfer material supplied to the photosensitive drum via a feeding unit and a conveyance unit and the like by a transfer device. The transfer material having the transferred toner image is conveyed to a fixing device by the conveyance unit. The toner image is subjected to heating and press-fixing. The transfer material is discharged to the outside of the main body of the image forming apparatus. Rotational drive is input into the photosensitive drum from the main body of the electrophotographic image forming apparatus during image formation operation. The toner conveyance stirring unit is also rotated and driven simultaneously with the rotational drive of the photosensitive drum.
Conventionally, in an electrophotographic image forming apparatus described above, when the internal temperature of the apparatus is remarkably increased, the deterioration of the developer is caused, and good development may not be obtained. To prevent the deterioration of the developer, a cooling fan is provided in the main body of the conventional electrophotographic image forming apparatus, to control the internal temperature increase of the apparatus.
Japanese Patent Application Laid-Open No. 2003-241624 discusses a technique in which airflow around the process cartridge caused by the cooling fan enters into the process cartridge from the ventilation hole of the side cover. The airflow passes through the vicinity of the developing roller, and is exhausted from an exposure window portion (laser opening). The airflow cools the surface of the photosensitive drum and the surface of the developing roller.
However, further size reduction and printing speedup of the electrophotographic image forming apparatus in the above-mentioned conventional technique cause the following problem.
The image forming apparatus includes an air course (airflow) so that air taken in by the cooling fan enters into the process cartridge from the ventilation hole formed in the side cover, passes along the vicinity of the photosensitive drum and the developing roller, and leaks to the exposure window portion (laser opening) and a transfer roller side.
However, the further size reduction and printing speedup of the electrophotographic image forming apparatus can be said to provide an insufficient cooling effect. Long-term or a large quantity of image formation operations increase a temperature of a toner in the developing device and near the developing roller.
The progress of temperature increase is further caused by residual heat from a heating source due to the process that a drive system in the apparatus stops after the image formation operation is completed, which requires a time until the temperature is sufficiently lowered. On this occasion, the deterioration of the toner is caused, and thereby a good image may not be obtained in the subsequent image formation.